The invention is broadly concerned with dispensing cartridges for viscous materials, particularly caulk, and more specifically involves plungers for such cartridges.
When filling caulk cartridges, it is common practice to close the cartridges by inserting a molded plastic plunger after the cartridge has been filled with the caulk material. It is desirable not to trap air in the cartridges during this operation, and a number of methods are currently used to address this concern. Vacuum may be used to draw air out of the cartridge prior to inserting the plunger. This method is effective, but time consuming. An alternate method utilizes a pin or spade-like device inserted between the cartridge wall and the plunger to create a temporary passage through which the air may escape as the plunger is inserted. Because of contamination by the caulk, it is necessary to stop this operation frequently and clean the pin or spade. A third method, attempts to distort the cartridge or plunger during insertion thereby creating an escape path for potentially entrapped air. This method is effective in removal of a large proportion of air, but frequently fails to allow the escape of all entrapped air.
A recent advance involves the incorporation of longitudinal ridges, either in the cartridge wall or plunger wall. These ridges function much as the pin or spade method, creating a passage between the cartridge and plunger through which air may escape. However, if the material is to be protected to provide a reasonable storage or shelf life in the cartridge, the ridges must not extend the full length of the plunger. There must result then, a compromise between extending shelf life and full evacuation of entrapped air.